This invention pertains to the art of cathodic protection methods and systems and, more particularly, to a deep well anode system for preventing corrosion of underground metallic structures by impressing electric currents thereon to make such structures cathodic with respect to the surrounding soil which functions as an electrolyte.
The invention is particularly applicable to a replaceable deep anode system received in a drilled hole and having a conductive polymer casing in an active anode area which provides improved electronic connection between the anode and the surrounding soil and which assures that the integrity of the drilled hole can be maintained during anode replacement. However, it will be appreciated to those skilled in the art that the invention can be readily adapted for use in other environments as, for example, where similar casing devices are employed to protect or house electrodes in other types of harsh environments.
The use of deep well ground beds or anode systems to introduce cathodic protection currents into the soil from an external electrical energy source to equalize or overcome the natural corrosion process of an underground or submerged metal structure is known in the art. Typically, such deep well ground beds comprise a drilled hole extending from the surface to a depth of in excess of fifty feet. Anodes are placed in the hole and impressed with electrical energy to generate the cathodic protection desired in the surrounding soil. However, variable geology of the surrounding soil makes such a construction substantially unreliable over along term and particularly expensive to replace as often the entire depth of the hole has to be redrilled. The failure of the anode connection or anode cable, in combination with irregular anode depletion has caused premature failures of these systems and generally unacceptable system life. Other problems with such systems have resulted from relatively poor electronic connection between the anode and the surrounding soil. Where current would flow through ambient fluids, such as water, gas bubbles have been generated which when accumulated form an insulating gas formation pocket which has contributed to system failure.
In order to overcome the cost ramifications of reinstalling a deep anode bed and drilling a new hole, and to overcome the problems of systems having a relatively unreliable system life, the industry has long sought a replaceable deep anode system in which the anodes could be selectively replaced and in which the integrity of the drilled hole could be maintained indefinitely. One attempt at such a replaceable deep anode is disclosed in U.S. Pat. No. 3,725,669 to Tatum. This patent discloses a replaceable anode casing received in a drilled hole having a continuous casing upper portion constructed of a non-conductive chemically inert material such as plastic and a lower portion constructed of a like material but including a plurality of openings to provide for the conduction of electrical current from an anode contained in the casing lower portion through ambient granular conductive material and ultimately out through the surrounding soil. However, such a system has suffered from a number of inherent problems. Specifically, the use of a non-conductive casing including a plurality of holes through which current can be transmitted provides a relatively large diameter casing with a restricted current path. The large diameter is required to accommodate the plurality of holes and retain the integral strength to house the granular material and maintain the integrity of the drilled hole during anode replacement. Related to the size problem is the economic consequence of such a construction in that the drilled hole, due to its large diameter, is relatively more expensive to make and the cost of materials for the casing and the granular fill is accordingly also greater.
The present invention contemplates a new and improved replaceable deep anode system which overcomes all of the financial and technological problems of conventional and replaceable deep anode systems to provide a new system which is simple in design, more economical to manufacture and install, readily adaptable to a plurality of dimensional characteristics, provides improved ease in anode replacement and improved cathodic protection in a replaceable deep anode system.